DE4443557A1 - Highly heat resistant, stress crack resistant polymethacrylate molding compounds - Google Patents

Abstract

Thermoplastic moulding materials (FM) with high transparency comprise compatible mixts. of (A) 1-99 pts.wt. of a copolymer (P) of (p1) 30-70 wt.% styrene and/or alpha -methylstyrene, (p2) 29-70 wt.% (1-6C alkyl) methacrylate and (p3) 1-20 wt.% (meth)acrylic acid, and (B) 99-1 pts.wt. of a PMMA polymer (PM) contg. (pm1) 80-100 wt.% methyl methacrylate (MMA) and (pm2) 0-20 wt.% comonomers. Pref. (P) is a copolymer of 30-55 wt.% (p1), 40-65 wt.% (p2) and 2-15 wt.% (p3). Pref. comonomer (p2) is MMA. Comonomer (pm2) in (PM) is (1-8C alkyl) acrylate, vinyl ester, vinylaromatic or (meth)acrylonitrile, pref. methyl acrylate. Polymers (P) and (PM) have mean mol. weights (MW) of between 10<4> and 5x10<5>. Material (FM) is a mixt. of 5-95 pts.wt. (P) and 95-5 pts. wt. (PM).

Description

Field of the Invention

The invention relates to highly heat-resistant, voltage Crack-resistant polymethacrylate molding compounds FM consisting of a compatible mixture of 1 to 99 parts by weight of one Copolymer P, composed of styrene and / or α- Methylstyrene, alkyl methacrylate with 1 to 6 carbon atoms in the ester residue and from acrylic and / or methacrylic acid with 1 up to 99 parts by weight of a polymethyl methacrylate PM, containing at least 80% by weight methyl methacrylate as Monomer units, the molding compositions FM being high Show transparency.

State of the art

DE-A 12 31 013 describes a process for the production of Copolymers described, which from 1 to 50 wt .-% of a α-alkylstyrene and 99 to 50% by weight of an alkyl methacrylate, optionally in minor amounts further polymerizable compounds, where am Structure of these copolymers 0.1 to 20% by weight Maleic anhydride and / or methacrylic acid are involved. Molding compositions made from such copolymers exhibit alternating exposure to hot and cold water low tendency to crack.

DE-A 23 41 123 encompasses thermoplastic molding compositions from 50 to 99 wt .-% styrene or alkyl methacrylate with 1 to  8 carbon atoms in the ester residue and from 1 to 50% by weight an α-substituted acrylic acid, for example Methacrylic acid, but at least 5% by weight of the acid must be present as acid anhydride. The transfer of a Part of the carboxyl groups in anhydride groups is replaced by a thermal treatment of the molding compound at one temperature reached above the Vicat softening point.

JP-A 83 125 712 describes molding compositions consisting of Co polymers from 50-98% by weight methyl methacrylate, 1 to 25 % By weight of styrene and 1 to 25% by weight of methacrylic acid with high Heat resistance and high resistance to thermal degradation.

EP-A 273 397 describes substrates for optical elements described, which consist of copolymers of methyl methacrylate, from aromatic vinyl compounds, from an unsaturated Carboxylic acid and from glutaric anhydride units consist of a good heat resistance and a high Show transparency.

US-A 2 851 448 claims transparent terpolymers which by chamber polymerization of monomer mixtures, consisting of vinyl aromatics, alkyl methacrylates and from unsaturated carboxylic acids, such as acrylic or methacrylic acid, in certain compositions, be preserved.

EP-A 264 508 describes a process for the production of Copolymers with high heat resistance described the thermal aftertreatment of the Copolymers of vinyl monomers such as styrene and methyl methacrylate and from acrylic or methacrylic acid Units. During thermal post-treatment arise from the (meth) acrylic acid units cyclic Anhydride units in the polymer chain.

Task and solution

The copolymers described in the prior art Alkyl methacrylates, vinyl aromatics and unsaturated Carboxylic acids are high quality molding compounds, what their heat dimensional stability and their corrosion resistance against affects various solvents. Therefore, there is great Interest, such copolymers with conventional Mix molding compounds to the properties of such To improve molding compounds. If you look at that Polymethyl methacrylate molding compounds as mixing partners, see above is a necessary prerequisite for the technical application such mixtures maintaining the high transparency of the Polymethyl methacrylate molding compound. Such mixtures must be thermodynamically compatible.

Mixtures of polymers are usually not sluggish. Despite a growing number of counterexamples, that have been found in recent years will become the Experiences of the expert still today from the following sentence determines: "Miscibility is the exception, immiscibility is the rule "(see: Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd. Ed., Vol. 18, page 460, J. Wiley, 1982).

Surprisingly, it has now been found that copolymers P consisting of:

(p1): 30 to 70% by weight of styrene and / or α-methylstyrene
(p2): 29 to 70 wt .-% alkyl methacrylate with 1 to 6 carbon atoms in the ester residue, and
(p3): 1 to 20% by weight of acrylic acid and / or methacrylic acid,
the sum of (p1), (p2) and (p3) making up 100% by weight,

in any weight ratio with polymethyl methacrylate Polymers PM, consisting of:

(pm1): 80 to 100 wt .-% methyl methacrylate and
(pm2): 0 to 20% by weight of monomers copolymerizable with methyl methacrylate, preferably from the group of alkyl acrylate with 1 to 8 carbon atoms in the ester radical, vinyl aromatics, vinyl ester and / or acrylonitrile or methacrylonitrile,

are thermodynamically compatible and transparent molding compounds Form FM.

The proportions in the copolymer P are preferably Comonomers (p1) at least 30 and at most 55 wt .-% (p2) at least 40 and at most 65% by weight and at (p3) at least 2 and at most 15% by weight. Particularly preferred are the proportions of comonomers in the copolymer P (p1) at least 30 and at most 50% by weight, at (p2) at least 45 and at most 60% by weight and at (p3) at least 3 and at most 10% by weight. The heat resistance of the Molding compounds FM, measured as Vicat softening temperatures VET according to DIN 53 460, are generally above 100 degrees C, preferably over 110 degrees C. The molding compounds are FM highly transparent and have a, from the mixing ratio of Copolymers P and PM dependent, glass transition temperature Tg on. In general, the average molecular weight weights Mw (weight average) of the copolymers P and PM  in each case between 10 5 and 5 × 10⁵, preferably between 3 × 10⁴ and 2.5 × 10⁵ daltons. (For the determination of molecular weights cf. for example H.F. Mark et al, Encyclopedia of Polymer Science and Technology, Vol. 10, pages 1 to 19, J. Wiley, New York, 1978).

The molding compounds are equally well resistant in Stress crack test against monomeric methyl methacrylate, against Petrol, against ethanol-water mixtures and against hot Water alternating with hot air (hot water change test).

Implementation of the invention The copolymers P and PM

The copolymers P consist of the monomer units (p1), (p2) and (p3). Examples of the monomers (p2) are called: ethyl methacrylate, propyl methacrylate, iso-propyl methacrylate, butyl methacrylate, iso-butyl methacrylate, Pentyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate and particularly preferably methyl methacrylate.

The preparation of the copolymers P is known Process for the polymerization of α, β-unsaturated compounds, in particular by radical polymerization, for example wise in substance, in solution or as a suspension polymerization carried out. As polymerization initiators can azo compounds such as Azodiisobutyronitrile, peroxides such as Dibenzoyl peroxide or dilauroyl peroxide, or redox systems serve, or the starting radicals can be radiation chemical generated (see, for example, H. Rauch- Puntigam, Th. Völker, "Acrylic and methacrylic compounds", Springer-Verlag, Heidelberg, 1967 or Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 1, pages 386ff, J. Wiley, New York, 1978).  

The copolymers P contain 30 to 70% by weight, preferably 30 to 55% by weight, particularly preferably 30 to 50% by weight of monomer units (p1), 29 to 70% by weight, preferably 40 to 65% by weight. %, particularly preferably 45 to 60% by weight of monomer units (p2) and 1 to 20% by weight, preferably 2 to 15% by weight, particularly preferably 3 to 10% by weight of monomer units (p3), the sum of the Parts of the monomer units make up 100% by weight. The average molecular weights M _{w of} the copolymers P are generally between 10⁴ and 5 × 10⁵ daltons, preferably between 3 × 10⁴ and 2.5 × 10⁵ daltons, correspondingly reduced viscosities η _spec / C, measured in accordance with DIN 51 562 in chloroform, of 10 up to 150 cm³g ^-1 , preferably 15 to 100 cm³g ^-1 . The molecular weights are adjusted by polymerizing the monomers in the presence of molecular weight regulators, such as in particular in the presence of the mercaptans known therefor (see, for example, Houben-Weyl, Methods of Organic Chemistry, Vol. XIV / 1, page 66, 1961 or Kirk- Othmer, Encyclopedia of Chemical Technology, Vol. 1, pages 296ff, J. Wiley, New York, 1978).

The copolymers P can be thermoplastic process crystal-clear, colorless moldings, the Vicat Softening temperatures VET according to DIN 53 460 from about 100 to 150 degrees.

For the manufacture and the average molecular weights of the Polymers PM applies to copolymers P above cited. As comonomer components (pm2) the Copolymers PM may be mentioned as examples: ethyl acrylate, Propyl acrylate, butyl acrylate, hexyl acrylate, octyl acrylate, α-methylstyrene, p-methylstyrene, vinyl acetate, vinyl propionate and preferably styrene and particularly preferred Methyl acrylate.  

Like the copolymers P, the polymers can also be used Process PM thermoplastic to crystal-clear shaped bodies, the Vicat softening temperatures VET from about 100 to 130 Grade C.

The molding compounds FM

The molding compounds FM are obtained by mixing the copolymers P made with the polymers PM, the type of mixture there are no limits.

Mechanical mixtures of the Mixture components P and PM, advantageously from Solids, such as granules or Bead polymers are used slowly running aggregates, such as B. drum, wheel, Double chamber or ploughshare mixers. The slow moving ones Mixing units cause mechanical mixing without that the phase boundaries are removed (cf. for example Ullmann's Encyclopedia of Technical Chemistry, 4th ed., Vol. 2, pages 282 to 311, Verlag Chemie, Weinheim, New York, 1980). The thermoplastic preparation takes place then by homogeneously mixing in the melt Use of heatable mixing units for the suitable temperatures, such as. B. in kneaders at 150 to 300 Grade C or preferably in extruders such as Single or multi-screw extruders or in Extruding with an oscillating screw and shear pins (e.g. in the Bussco kneader).

In a further process, the Molding compounds FM, for example, polymer PM in the Monomer mixture (p1), (p2) and (p3) are dissolved,  the copolymer P in the presence of PM Polymerization is made.

The characterization of the polymer according to the invention Mixtures as compatible mixtures are made according to the recognized criteria (see Kirk-Othmer, loc.cit., Vol. 18, pages 457 to 460; Brandrup, Immergut, polymer Handbook, 2nd. Ed., Abs: III, page 211, Wiley Interscience, New York, 1975).

In the case of the compatible polymer mixtures (molding compositions) FM, a refractive index and a single glass transition temperature Tg are observed, which is between those of the two mixture components P and PM. As a further indication of the compatibility of the polymer mixtures FM, the occurrence of the LCST (Lower Critical Solution Temperature) is used, the existence of which is due to the fact that the transparent mixture, which had been clear until then, separates into different phases and due to the different refractive indices of the mixture components P and PM becomes optically cloudy. This method provides clear evidence that the original polymer mixture consisted of a single homogeneous phase in thermodynamic equilibrium (see, e.g., BDR Paul, Polymer Blends & Mixtures, pages 1 to 3, Martinus Nÿhoff Publishers, Dordrecht, Boston, 1985). For this purpose, the cloud point T _Tr (cloud temperature) is determined experimentally, for example on a Kofler heating bench (cf. Chem. Ing. Technik, 1950, pages 289ff).

Beneficial effects

The compatible polymer mixtures FM according to the invention according to claim 1 can already due to their  Compatibility claim the interest of technology. The FM molding compounds are usually crystal-clear and highly transparent. The heat resistance of the polymers PM is determined by the alloying of the copolymers P is generally increased. Another important advantage, especially for the The FM molding compounds are used in the automotive sector high resistance to stress corrosion cracking in the following Media on:

• - Monomeric methyl methacrylate, for example when joining interior and exterior luminaires Automotive tail lights during the so-called Mirror welding process from the polymers PM is released
• - Ethanol / water mixtures, such as those as an antifreeze in cleaning liquids be used for automotive windows, as well
• - Fuels for internal combustion engines, such as for example, unleaded gasoline with high Octane number.

The media listed have a wide range their polarity. It was all the more surprising that the excellent in the molding compositions FM according to the invention Resistance of the polymers PM to fuels in high Dimensions is obtained while the resistance of the Molding compounds FM against monomeric methyl methacrylate and against Ethanol / water mixtures compared to those of Polymer PM is generally significantly increased.  

On the other hand, copolymers P have high The proportions of monomers (p1) are generally lower Resistance to petrol based on Alloying of the polymers PM generally clear is increased.

The molding compositions FM according to the invention thus have numerous synergistic combinations of the individual properties of the Mixture components P and PM. It is also advantageous the recyclability of components made of molding compounds FM, the for example after granulation together with granulated Components made of polymer PM to transparent, high heat dimensionally stable molding compounds can be processed in turn used as injection-molding compounds can be. The properties are also advantageous of the molding compositions FM according to the so-called Hot water change test, which the stress of Materials, for example in the sanitary area Switching between water and air storage simulated. In order to FM molding compounds are also for the household sector excellently suited.

The following examples serve to explain the Invention.

• 1. LCST by measuring the cloud point T _Tr on the Kofler heating bench (see above).
• 2. Vicat softening temperature VET in degrees C. DIN 53460.
• 3. Reduced viscosity η _spec / C in chloroform according to DIN 51562
• 4. Viscosity of the polymer melts n _s according to DIN 54811
• 5. Glass transition temperature Tg by differential thermal analysis (DSC, see above)
• 6. Average molecular weight M _w by gel permeation chromatography (see above).
• 7. Stress crack resistance:
  Extruded sheets are made from the molding compounds FM, from which test specimens measuring 230 × 20 × 4 mm are machined. The surface of the test specimens is cleaned with water containing surfactant and the test specimens are stored for 4 days at 23 degrees C and 50% RH before the test procedure.

Inspection process

The cleaned test specimens are at 20 MPa Bending stress at 23 degrees C. After that the surface of the test specimen with the test media, such as monomers or fuels completely wetted and the time t until breakage the test specimen is determined.

• 8. Hot water change test:
  Test specimens measuring 230 × 20 × 4 mm are in turn injection molded from the molding compounds FM. Before the start of the test, the test specimens are stored at 23 degrees C and 50% rh for at least 1 week.

A change consists of:

• 1. Immerse the test specimen in demineralized water an initial temperature of 65 degrees C and 8- hourly storage of the test specimen in the VE Water spilled on space during this period temperature cools.
• 2. Drying the sample in the heat for 16 hours cabinet at 50 degrees C.

There will be the number of changes until occurrence of the first cracks that are visually perpendicular to the Spray direction are determined, determined.  

Examples example 1 Preparation of the copolymer P1

A monomer mixture of 5500 g methyl methacrylate, 3500 g Styrene and 1000 g of methacrylic acid are used as the polymerization initiators 20 g dilauroyl peroxide and 5 g 2,2-bis (tert.- Butylperoxy) butane and as molecular weight regulator 27 g tert- Dodecyl mercaptan added. This solution is in one Polymerization chamber first over dry ice for 15 Minutes by applying a vacuum from Oxygen free. Then in a water bath for 2.5 hours Polymerized 60 degrees C and 36 hours at 50 degrees C. For Final polymerization is then carried out in the chamber Drying oven annealed at 120 degrees C for 12 hours.

The polymer P1 has the following properties:
η _spec / C = 72 cm³g ^-1
M _w according to Mark-Houwink from η _spec / C with PMMA as calibration standard:
165,000 daltons
VET: 120 degrees C.
Tg: 121 degrees C.
Hot water change test: 96 changes
Stress crack resistance (until the specimen breaks):

• a) against methyl methacrylate: 799 s
• b) against ethanol / water = 75/25: 278 s
• c) against unleaded premium gasoline: 158 s

Examples 2 to 6

Production of mixtures of copolymer P1 and Plexiglas ® molding compound Y8N (copolymer of 99% by weight methyl methacrylate and 1% by weight methyl acrylate, M _w ≅ 110000 daltons).

The mixtures of copolymer P1 and Plexiglas® molding compound Y8N are produced by mechanical mixing of the granules of the individual components and subsequent melt mixing in a single-screw laboratory extruder. The tape extrudate is used as a test specimen for the visual assessment of the compatibility as well as for the determination of the separation temperatures (T _Tr ) and the heat resistance (Tg, VET).

Examples 7 to 10

Characterization of mixtures of copolymer P1 and Plexiglas ® molding compound Y8N with regard to stress crack resistance and hot water change test.

Claims (8)

1. Thermoplastic molding compositions FM with high transparency consisting of compatible mixtures of 1 to 99 parts by weight of a copolymer P, composed of:
(p1): 30 to 70% by weight of styrene and / or α-methylstyrene
(p2): 29 to 70% by weight of alkyl methacrylate with 1 to 6 carbon atoms in the ester radical, and
(p3): 1 to 20% by weight of acrylic acid and / or methacrylic acid,
the sum of (p1), (p2) and (p3) making up 100% by weight,
as well as from
99 to 1 part by weight of a polymethyl methacrylate polymer PM, composed of
(pm1): 80 to 100% by weight of methyl methacrylate, and
(pm2): 0 to 20% by weight of monomers copolymerizable with methyl methacrylate. 2. Thermoplastic molding compositions FM according to claim 1, characterized in that the copolymer P is composed of:
30 to 55% by weight (p1), 40 to 65% by weight (p2) and 2 to 15% by weight (p3). 3. Thermoplastic molding compounds FM according to the Claims 1 and 2, characterized in that the comonomer (pm2) is selected in the polymer PM is from the group alkyl acrylate with 1 to 8 Carbon atoms in the ester residue, vinyl esters, Vinyl aromatic, acrylonitrile and / or methacrylonitrile. 4. Thermoplastic molding compounds FM according to the Claims 1 to 3, characterized in that the comonomer (p2) in the copolymer P Is methyl methacrylate. 5. Thermoplastic molding compounds FM according to the Claims 1 to 4, characterized in that the comonomer (pm2) in polymer PM Is methyl acrylate. 6. Thermoplastic molding compositions FM according to claims 1 to 5, characterized in that the average molecular weights M _{w of} the copolymer P and the polymer PM are between 10⁴ and 5 × 10⁵ daltons. 7. Thermoplastic molding compounds FM according to the Claims 1 to 6, characterized in that it from mixtures of 5 to 95 parts by weight Copolymer P and 95 to 5 parts by weight Polymer PM exist. 8. Use of the thermoplastic molding compounds FM according to claims 1 to 7 for the production of Molded articles.